1. Field of the Invention
This invention relates generally to flexible polyurethanes. More particularly, this invention relates to highly filled, flexible polyurethane foams.
2. Brief Description of the Prior Art
High-density polyurethane foams and solid polyurethanes are useful materials for a wide variety of applications, particularly sealing gaskets for electronic devices. These foams preferably have densities in the range from about 10 to about 65 pounds per cubic foot (pcf). It is also important that the foams have acceptable compression set, compressive force deflection, tensile strength, elongation, tear strength, low outgassing, and non-corrosiveness.
While a number of prior art foams meet the above requirements, such as the PORON(copyright) foams sold by Rogers Corp., Rogers, Conn., it has heretofore been difficult to impart good or excellent flame resistance to such foams. For example, many commercial products must presently meet standards of flame resistance as measured by the test procedure set forth in Underwriters Laboratories, Inc.(copyright) Bulletin UL-94, Test for Flammability of Plastic Materials for Parts in Devices and Appliances, Fifth Edition from Oct. 29, 1996, incorporated herein by reference in its entirety. Of particular interest are xe2x80x9c20 mm Vertical Burning Test; V-0, V-1, or V-2xe2x80x9d and xe2x80x9cHorizontal Burning Foamed Material Test; HBF, HF-1, or HF-2xe2x80x9d. A rating of UL 94 V-0 or HF-1 is often specified for foams that are used in components located close to power sources.
The preparation of low density, flexible polyurethane flame-retardant foam compositions are generally well known as evidenced by the prior art. U.S. Pat. No. 4,022,718 teaches the preparation of high resilience cold-cured polyurethane foams incorporating 2,3-dibromo-1,4-butenediol as a chain extender and flame-retardant component. U.S. Pat. No. 4,147,847 teaches a method of preparing flexible, flame-retarded, polyurethane foams by employing specific foam stabilizers, which reduce the required amount of normal flame-retardant additives. U.S. Pat. No. 4,162,353 teaches the preparation of flexible polyurethane foams incorporating therein a halo-substituted alkyl phosphate such as tris(2-chloroethyl)-phosphate and an unsubstituted trialkylphosphate such as triethylphosphate. U.S. Pat. No. 4,849,459 describes a flame retardant flexible polyurethane foam comprising the reaction product of a polyether polyol and a toluene diisocyanate and incorporating melamine and another flame retardant. All of the foregoing are incorporated herein by reference.
While suitable for their intended purposes, the above-described flexible polyurethane foams are low density, have lower tensile strength, lower tear strength, lower compressive force deflection, and poor compression set resistance. Because of these deficiencies, these low-density prior art foams are not suitable for use as gaskets. Consequently, there is a need for a high-density polyurethane foam composition, which is highly flame retardant, and yet which still retains the required degree of compression set, compressive force deflection, tensile elongation, tear strength, low outgassing, and non-corrosiveness.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a composition for the formation of a flame retardant polyurethane foam comprising an organic polyisocyanate component, an active hydrogen-containing component reactive with the polyisocyanate component, wherein the active hydrogen-containing component preferably has an overall viscosity of less than about 500 centipoise, a catalyst component, a surfactant, and a flame retarding composition comprising an antimony-based compound, a halogenated, active hydrogen-containing component reactive with the polyisocyanate component, and a halogenated flame-retarding agent, preferably wherein the composition, without the polyisocyanate component, has a viscosity of less than about 8,000 centipoise prior to foaming. Preferred antimony-based compounds include antimony trioxide, preferred halogenated, active hydrogen-containing components include liquid brominated diols, and preferred halogenated flame-retarding agents are solid, bromine-containing organic compounds.
The components may be low VOC in order to provide low fogging and low outgassing. Accordingly, in another embodiment, a composition for the formation of a flame retardant, low outgassing, low fogging polyurethane foam comprises a low VOC organic polyisocyanate component, a low VOC active hydrogen-containing component reactive with the polyisocyanate component, wherein the active hydrogen-containing component preferably has an overall viscosity of less than about 500 centipoises, a catalyst component, a surfactant, and a flame retarding composition comprising a halogenated, active hydrogen-containing component reactive with the polyisocyanate component, preferably wherein the composition, without the polyisocyanate component, has a viscosity of less than about 8,000 centipoises prior to foaming.
Such foams have a UL-94 rating of V-1 and/or HBF. Even more preferably, foams having a thickness of about 31 to about 250 mils and a density of about 15 to about 30 pcf have a UL 94 V-0 rating, and foams having a thickness of about 28 to about 40 mils and a density of about 15 to about 30 pcf have a UL 94 V-0 rating. The foams have excellent physical properties, low outgassing (preferably less than 1% by weight), and non-corrosivess.
Because of the foregoing features and advantages, the materials described herein are especially suitable where flame retardant cushioning is desired, for example as gaskets for electronic and automotive applications. The above discussed and other features and advantages will be appreciated and understood by those skilled in the art from the following detailed description.